1. Field of the Invention
This invention relates to a delayed coking process in which small amounts of cracking catalyst and hydrogen are added to the coker feed to improve the distillate yield and decrease the coke make.
2. Description of the Prior Art
Delayed coking is a well-known oil refining process that is used to convert heavy hydrocarbon feedstocks into lighter hydrocarbon products and coke. In this process the heavy hydrocarbon feed is heated rapidly to cracking temperatures and fed into a coke drum. The heated feed soaks in the drum in its contained heat which is sufficient to convert it into cracked vapors and coke. The cracked vapors are taken overhead and fractionated, with the fractionator bottoms usually being recycled to feed. The coke accumulates in the drum until the drum is filled with coke, at which time the heated feed is diverted to another coke drum while the coke is removed from the filled drum.
Numerous coking processes are described in the patent literature in which the coker feed is first hydroprocessed to remove metals or sulfur before being fed to the coker furnace. See, for instance, U.S. Pat. Nos. 2,871,182, 2,963,416, 3,617,487, 3,817,853, and 3,684,688.
It is also known to use the residuums from catalytic cracking processes as a feed to delayed coking processes. U.S. Pat. No. 3,326,796 teaches a process for making electrode grade coke by subjecting such residuum to delayed coking.
U.S. Pat. No. 3,619,413 describes a delayed coking process in which small amounts of hydrogen halide or hydrocarbyl halides are added to the heated feed to the coke drums. The addition of such halides is alleged to make the volatile content of the coke more uniform without affecting the distillate yield adversely.
U.S. Pat. No. 4,169,041 describes a fluid hydrocoking process in which metallic hydrogenation catalysts, particularly molybdenum, chromium, and vanadium are added to the fluid coking feedstock. The addition of such metals is reported to increase distillate yield and reduce coke yield. U.S. Pat. Nos. 2,888,393 and 2,888,395 also teach the use of hydrogen and hydrogen plus catalyst, respectively, in fluid coking.